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I am using arduino nano GPIOs to switch multiple devices (16 devices) using MOSFET (IRF540N).

I have configured my switching circuit in such a way that my device will remain ON even if even if high signal is not given to but to switch off those devices nano needs to give LOW signal (I have implemented this circuit using resistor divider).

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My requirement is to keep the devices on even if nano is not powered which is been achieved only when one device is connected but 2 or more devices are connected then devices are switched off.

I am also isolating the GNDs of nano and devices using relay.

Still my devices are getting Off when multiple devices are connected? Is it because of even if both the GNDs are isolated some amount of current flowing via nano controller internally?

Is there any other solution to achieve the same?

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    \$\begingroup\$ Put a pull-down resistor (e.g. 100k) on the gates of those MOSFETs. \$\endgroup\$ Commented Feb 22, 2018 at 10:13
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    \$\begingroup\$ As an aside, the IRF540 is a really poor choice for this as it requires a much higher Vgs that the Arduino can supply. Look for a logic-level MOSFET instead. \$\endgroup\$ Commented Feb 22, 2018 at 10:27
  • \$\begingroup\$ Use the IRL series of mosfets instead. These can be driven directly from an arduino \$\endgroup\$ Commented Feb 22, 2018 at 15:05

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Firstly, isolating the grounds between the Nano and the MOSFETs is a recipe for disaster. The MOSFETs have a high impedance gate input and when you isolate the grounds that gate voltage will float to some value that is indeterminate. You could easily destroy the MOSFET with gate-source breakdown. As for a solution, consider this: -

schematic

simulate this circuit – Schematic created using CircuitLab

With no signal produced by the Nano, M1 will be turned off and M2 turned on by the gate being pulled-up to the load_power_rail. To turn off the load-switch (MOSFET M2), the nano needs to apply 3.3 volts to M1's gate relative to ground/0 volts.

Choose MOSFET M1 so that it is a logic level switching device.

If necessary (it usually is) use a reverse protection diode across the load terminals to prevent inductive spikes destroying M2.

When using multiple channels of this circuit, all loads must share the same common ground/0 volts.

If this is a problem then you will need to use opto-isolation instead of M1.

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